A numerical modeling study of the microphysical processes leading to tropical cyclogenesis under different environmental conditions

Although recent advances in observational techniques coupled with the ever-increasing sophistication of numerical models has helped shape our knowledge of developing and mature tropical cyclones, important questions regarding the pre-genesis phase largely remain unanswered. As we face the possibility of global climate change, it's imperative that we understand the physical processes responsible for storm formation before making predictions as to how tropical cyclone frequency will be affected by a warming environment. In addition, gaining a better understanding of the pre-genesis phase could help forecasters identify which tropical disturbances will develop into mature tropical cyclones. This could translate into a significant increase in lead time for emergency management personnel, especially for storms forming in close proximity to coastal areas.

In this paper an ongoing modeling study to better understand the pre-genesis processes in tropical cloud clusters is described. The model used to facilitate this process is the Weather Research and Forecasting (WRF) model developed at the National Center for Atmospheric Research. While several recent tropical cyclogenesis studies have utilized simulations under idealized environmental conditions, this study analyzes the processes leading to genesis for several real-life cases. In this paper we present an analysis of the convective structure and microphysical evolution of the pre-genesis cloud clusters from two of these case studies. Even though the pre-genesis environments differ somewhat between simulations, striking similarities exist in the early convective structure as convective bursts appear to precede genesis in each simulation. Our findings suggest that the stratiform precipitation regions that develop after the pre-genesis convection play a significant role in preconditioning the atmosphere for genesis by concentrating mid-level potential vorticity regardless of what the background, large-scale conditions are.